Nucleation and growth studies of large-area deposited WS2 on flexible substrates

Abstract

Transition metal dichalcogenides (TMDCs) such as tungsten disulfide (WS _2 ) are studied for advanced electronic and optical devices because of their unique and versatile electrical, optical and mechanical properties. For the use of TMDC films in next-generation flexible electronics, large-area bottom-up synthesis on flexible substrates needs to be mastered, understood and controlled. In this study, we performed a detailed study on the nucleation and growth of WS _2 layers deposited by metalorganic chemical vapor deposition (MOCVD) on crystalline van-der-Waals material muscovite mica as a model substrate and on the alkali-metal free flexible glass AF 32 ^® eco . The deposition of the WS _2 layers was performed using an all nitrogen-coordinated bis-imido-bis-amido tungsten based precursor in combination with elemental sulfur as the co-reactant. On both substrates, crystalline growth of WS _2 at a moderate growth temperature of 600 °C was verified by Raman spectroscopy and X-ray diffraction (XRD). However, the growth mode and nucleation density differ significantly. On mica, an initially planar growth of WS _2 triangular islands is observed, whereas untreated glass reveals an out-off plane growth. Detailed XRD and Raman analysis show tensile strain in the WS _2 films on both substrates, indicating a strong interaction from CVD grown TMDC films with the underlying carrier material. In order to avoid such substrate-semiconductor interaction, a substrate pre-treatment is required. A plasma pre-treatment prior to the deposition leads to a planar growth even on amorphous glass substrates.

Keywords

• WS2
• nucleation
• mucvovite mica
• flexible glass
• CVD
• large-area growth